This invention relates generally to computer systems and more particularly to power systems used in computers.
As is known in the art, computer systems have become ubiquitous. Computer systems generally include a central processing unit, memory and I/O devices all of which are packaged together typically on a plurality of printed circuit boards which are disposed within a common computer system cabinet. In order to function, these circuit boards are provided with D.C. power from a D.C. supply, and the D.C. power is distributed to the electrical circuits on the printed circuit board.
One of the principal considerations which drive improvements to computer system hardware is to increase the speed of the computer system hardware. Speeds are increased using various techniques including scaling of standard semiconductor processing techniques to provide scaled semiconductor devices, that is devices having smaller geometries i.e. dimensions. In particular, one type of scaling arrangement used for computer devices requires that the power supply voltages fed to the devices be reduced in magnitude from the voltage provided to unscaled devices in order to increase the reliability of the devices. Scaling of logic devices has led to the need for multiple power supplies in high performance computer systems. Other system requirements have also led to the need for multiple power supplies.
Several techniques are known for providing power to computer system devices. In prior techniques, a large power supply which converted illustratively 117 A.C. volts into 5 volts or other D.C. voltages was provided in the cabinet of the computer system. The voltages were then distributed via a power bus to each of the modules in the computer system. Newer techniques referred to as "distributed power techniques" use a D.C. power supply supplied via an appropiate line voltage. This DC supply is at a relatively high DC voltage illustratively 48 volts. This high voltage, however, is at a relatively low current level and is distributed to each printed circuit board in the computer system. On each printed circuit board is at least one DC to DC converter which locally converts the input high level DC voltage to at least one low level DC voltage for use by the electric circuit devices on the module.
A problem arises when modules and systems contain both scaled or low voltage circuits and standard higher voltage circuits. For example, many modern computer systems are fabricated with logic devices which require both 5.0 volt and 3.3 volt supplies to feed the logic devices within the system. In certain types of semiconductor processing it is an artifact of the processing that for the 3.3 volt supply logic devices an input signal to the device from the 5 volt supply logic can destroy the 3.3 volt logic devices unless the 3.3 supply voltage is present at the power input of the 3.3 logic device prior to application of the input signal.
This problem leads to the necessity of designing a power sequencer for a power system which controls timing of operation of the power converters during turn on of the system. Accordingly, in order to prevent damage to the logic devices, it is necessary to bring the DC to DC converters to operating voltages in a controlled and known sequence.
A further problem may arise in retrofit designs or where a newer design is to use existing components of a previous design and where the provision for only one enable signal is provided to control both the 3.3 and 5.0 DC to DC converters turn on to operating voltage levels in the desired sequence.
Additional problems also arise to insure that during failure of the 3.3 volt supply or converter or during short circuiting of the 3.3 volt supply or converter that the 5 volt supply or converter shuts down before the 3.3 volt supply completely fails. In the event that this does not happen, the aforementioned problems of destruction the 3.3 volt logic will still occur.